1. Field of the Invention
The present invention relates to improvements in a gas shield chamber used in the welding of rails by gas shielded arc welding.
2. Description of the Prior Art
When welding rails by gas shielded arc welding, it has been usual in the past so that after the butt welding area of the rails have been surrounded on all sides by a gas shield chamber thus shielding the welding area from the atmosphere, a shielding gas is injected around the welding area inside the chamber and the arc welding is effected in this gas atmosphere by a welding nozzle.
In one of the prior art gas shield chambers used for this purpose, the gas shield chamber comprises a chamber casing having one side opened and the other five sides enclosing the front, back, top and lateral sides of the welding joint of rails and a back cover placed in contact with the bottom surfaces of the rails at the welding joint through a backing plate and adapted to close the open side of the casing. Also, disposed inside the casing are a pair of side backing plates or blocks which are movable toward and away from the welding joint of the rails for contact with the sides thereof so as to prevent the weld metal from leaking and dropping from the welding joint during the welding of the webs and heads of the rails at the welding joint. Each of the side backing plates is mainly made of copper and formed therein with a cooling water flow path so as to be cooled with water supplied from the outside. Also, each of the side backing plates is provided with a plurality of shielding gas jets so that the side backing plates inject the shielding gas, along with a separate shielding gas injector arranged in the uppart of the chamber, into the chamber during the welding and the arc welding is performed in this gas atmosphere by a welding nozzle.
However, this prior art gas shield chamber involves a number of problems which will be described hereunder. The problems include the following.
(a) Since the screw shafts for moving the side backing plates are positioned above the welding area within the chamber, during the welding the spatter and fume tend to deposit on the shafts and this impedes the movement of the side backing plates.
(b) Due to the mechanism in which the screw shafts are arranged within the chamber and they cannot be touched from the outside, the screw shafts cannot be operated manually and moreover the side backing plates cannot be moved independently with each other.
(c) It is difficult to control the injection rate of the shielding gas so that during the welding the arc is disturbed if the injection rate is excessively large and the gas shield becomes insufficient if the injection rate is excessively small.
(d) Each of the side backing plates is formed with an excess weld metal or bead depositing groove at its portion adapted to contact with the welding groove and therefore there is the danger of causing an incomplete penetration at the boundary area between the webs and heads of the rails depending on the shape of the excess bead depositing grooves.
(e) While the ground line is connected from the welding power source to the chamber back cover, the ground point is provided on the one side only, and thus there is the danger of deflecting the welding arc to the opposite side to the ground point due to the effect of the deflected magnetic blow and thereby causing a defect such as an overlap etc. on the ground point-side portion of the surface of the boundary area between the webs and flanges of the rails.
(f) It is necessary to attach by welding, tape or the like a weld metal leakage preventing tab to each side of the rail flanges at the welding area and this operation requires a considerable time.
(g) The production of an excellent backing bead will be made difficult due to poor contact between the backing plate and the bottom surfaces of the rails.
(h) The hoses for the shielding gas and cooling water are connected at a number of points and the attachment of the hoses requires a considerable time.